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SubjectRe: [PATCH RFC] x86/tsc: Make recalibration default on for TSC_KNOWN_FREQ cases
On Mon, May 22, 2023 at 01:49:53PM +0200, Thomas Gleixner wrote:
> On Mon, May 22 2023 at 16:47, Feng Tang wrote:
> > On Mon, May 22, 2023 at 10:14:08AM +0200, Thomas Gleixner wrote:
> >> On Mon, May 22 2023 at 11:30, Feng Tang wrote:
> >> Are any of these affected platforms shipping already or is this just
> >> Intel internal muck?
> >
> > Paul and Rui can provide more info. AFAIK, those problems were raised
> > by external customers, so the platform were already shipped from
> > Intel. But I'm not sure they are commercial versions or early
> > engineering drops.
>
> So its at a company which knows how to update firmware, right?

Yes. And the recalibration may help to exposed the bug quickly.

> >> So why do you force this on everyone?
> >
> > How about we keep the optional parameter, and enforce the check for
> > bare metal platforms which got TSC frequency info from CPUID(0x15),
> > like:
>
> What prevents a hypervisor from providing this info in CPUID(0x15)?
>
> > @@ -670,8 +670,10 @@ unsigned long native_calibrate_tsc(void)
> > * frequency and is the most accurate one so far we have. This
> > * is considered a known frequency.
> > */
> > - if (crystal_khz != 0)
> > + if (crystal_khz != 0) {
> > setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
> > + tsc_force_recalibrate = 1;
> > + }
> >
> > /*
> > * Some Intel SoCs like Skylake and Kabylake don't report the crystal
>
> and five lines further down:
>
> /*
> * For Atom SoCs TSC is the only reliable clocksource.
> * Mark TSC reliable so no watchdog on it.
> */
> if (boot_cpu_data.x86_model == INTEL_FAM6_ATOM_GOLDMONT)
> setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE);
>
> So its reliable and needs recalibration against hardware which does not
> exist.

I misunderstood it. When you said 'SOCs which lack legacy hardware',
I thought you were referring those old Merrifield/Medfield things,
which may have no HPET/ACPI PM_Timer but an APB timer, and mainly go
through MSR way (tsc_msr.c) for TSC frequency.

In this native_calibrate_tsc(), which touches the INTEL_FAM6_ATOM_GOLDMONT
and INTEL_FAM6_ATOM_GOLDMONT_D, I dug out one Apollo Lake and one
Denverton platform (which comply to those GOLDMNOT model), and they
both have 'hpet' and 'acpi_pm' clocksource registered.

Thanks,
Feng

>
> Thanks,
>
> tglx

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